Impact tool



Jan. 19,1932. L. A. SCHMIDT 1,841,553

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Jan. 19, 1932..

L. A. SCHMIDT IMPACT TOOL Filed July 14. 1927 8 Sheets-Sheet 2 3% TmR/VEY Jan. 19, 1932. L. A. SCHMIDT 1,841,553

IMPACT TOOL Filed July 14, 1927 a Sheets-Sheet s E??- ll]? 297 33 I I I /v vzzv'rol? J Zuzana/ZR W TNESS BY 97W 152 I Jan. 19, 1932. V A. SCHMIDT IMPACT TOOL Filed July 14. 1927 23 9; 241 5;; 3: zzs 31% 5 8 Sheets-Sheet 4 Jan. 19, 1932. H Y SCHMIDT 1,841,553

IMPACT TOOL Filed July 14, 192' 8 Sheets-Sheet 5 T T'T C LT/-1- zas 2751 31 285 z: W v 8 a 71 3P0 .273 '17 o 9 575 23g 2 ,276

INVE/YTOIi Jan. 19, 1932. SCHMIDT 1,841,553

IMPACT TOOL Filed July 14. '1927 8 Sheets-Sheet 6 Q4 W/TNE:55 J

Jan. 19, 1932. h SICHWDT 1,841,553

IMPACT TOOL Filed July 14, 1927 8 Sheets-Sheet '7 INVENTOI? VITA/55 1 5r Jan. 19, 1932. L. A. SCHMIDT 1,841,553

IMPACT TOOL Filed July 14. 1927 8 Sheets-Sheet 8 fizz g. Z51

I l l l INYENTOI? WITNESS W Y I 5% v flTTO/iNY Patented Jan. 19, 1932- UNITED J STAT-E15} PA-T NT OFFICE mom A. scmum', or rouenxmsm, nnw Yonx', ASSIGNOB ro riinnsnvmn ensonmn nmx. conrnnr, A conrom'rron or nmwnan' MAUI TOOL A licationfiled July 14,

My invention relates to a gasoline operated drill, hammer or similar impact tool or device in which a unitary iston or piston-hammer is reciprocated within a cylinder on the principle of a two-cycle internalcombustion' I i Ti lie structure forming the subject-matter of my invention includes a unitary cylinder comprising three coaxially alined parts, rig-.

idly secured together and within which the impact-piston or"piston-hammer is recipro cated on the princlle of a single-sctin twocycle' internal com ustion engine, inso or as 1g air is drawn by the piston orpiston-hammer through a'carburetor into a mixing and trans fer chamber on the non-working or compr'es sion stroke of the piston-hammer; is trans- 'ierred, under pressure atthe end or" the workas in stroke to the combustion end of the cylin or to expel the roducts of combustion remaining in the cylinder from the previous working stroke; is compressed within the combustion chamber durin the non-worln'ng so or compression stroke and is e 7 end of the compressionstroke y a suitable ignition-device or system to impel. the piston or iston-hammer forwardly to sheet the wor ing stroke and toproduce an impact of the piston-hammer against a tool appro' riately mounted in or at the end of the cylin er. The present invention relates to the type of percussion toolwhich forms the invention of Letters Patent of the United States Number 1,508,623, granted September 16, 1924, to Charles Stuart Somervell, and comprises certain improvements therein, whercb the construction is somewhat simplified, t e o erstion of the mechanism-rendered more e cien't and the structure is more durable. In percussive tools of this t e the piston or piston-hammer is reciprocate d rapidly and the blow upon the tool or stripe-pin is heavy and sharp, with the result that the parts of 50 said drill to which the blows are imparted or other means for circulatin loded at the and dispersing area as is 1827. Serial No. 205,981.

communicated and by which the shocks are absorbed,'must withstand such strains and vibrations over a relatively "long period of time. i

The explosion end of the cylinder in this type of tool tends to become very hot, for t e weight ofa water-cooling system for the cylinder would greatly detract from the utility of the drill as a portable mechanism. The cylinder and the parts heated thereby must be air cooled by mereradiation, for a fan or a current of air over and around the cylin er would seriously interfere with the manipulation of the tool and add tothe weight of the tool. But the air cooling of the cylinder and piston by conducting the heat of combustion by static radiation is arelatively ineflicient method of. reducing the temperature of the metal 0 linder with the result that, the piston an the explosion end of the cylinder and the cylinder head are required to operate at much higher temperatures than those to which ordina internal combustion engines are subjects It is, therefore, one of the objects of the present invention to provide a cylinder construe tionwherein asmu'ch as possible of the heat of the piston head is conducted directly to the walls of the combustion chamber, to rovide these walls with as great a heat con noting. ossible, and to make that orti'on of the cy inder of a steel which has n heat-treated so that it will withstand and operate satisfactorily under high temperature conditions. v

A further object of m invention is to heat-treat that. portion of t e cylinder which is subjected to the sharp, rapid impact of the piston-hammer and in sucha manner as to make it stand up without crystallization for a long period of time. The portion of the cylinder forming the combustion or explosion chamber and the part of the cylinder which is subjected to the severe shocks and blows above-mentioned are located at opposite ends of the unitary cylinder structure and upon the intermediate portion is mounted a rotor, preferably concentric with the axis of the cylinder and of the piston-hammer, as shown in the Somervell patent above referred 10!) to. It is through this intermediate portion that the cross-head carried by the pistonhammer projects and in which the cross-head is slidingly mounted for reciprocation, and the ends of the cross-head are in engagement with the cam carried by the said rotor by means of which the reciprocatory rectilinear motion of the piston-hammer is converted into the rotary movement of the rotor to effect the return or compression stroke of the piston. This intermediate portion is subjected to torsional strains about its axis, in addition to being required to absorb some of the shocks imparted to the impact end of the cylinder and some of the heat conveyed thereto from the combustion end of the cylinder. It is, therefore, a further object of my invention to heat-treat the metal of said intermediate portion in such a manner as to make it capable of best withstanding the peculiar strains to which it is subjected.

A. further object of my invention is to provide a construction wherein that portion of the cylinder, including the combustion chamber and the adjacent intermediate portion upon which is mounted the rotor, may be used without any change whatever in their construction with either oftwo different types or kinds of impact sections, (1) an impact section providing a fuel intake and transfer chamber and an air compression chamber and (2) another impact section providing only a fuel intake and transfer chamber.

A further object of my invention is to provide a construction wherein a uniform explosive mixture may be formed and maintained during the continuous action of the drill. It is the object of my invention to draw the air for the explosive mixture through the carburetor into the mixing chamberand then to discharge the mixture at the end of the working stroke out through the same port over or through the carburetor but without adding to the mixture more gasoline or similar fuel, with the result that substantially all the air is discharged from the cylinder during each stroke and out through the same port by which it entered so that a fresh supply of uniform explosive mixture is drawn into and delivered from the mixing and transfer chambers on every complete reciprocation of the piston-hammer.

A further object of my invention is to provide adequate means to air-cool the pistonhead, the cylinder head, and the walls of the explosion chamber without substantially adda ing to the weight of the drill as a whole.

A further object of my invention is to provide replaceable means carried by the piston rodto adjust the fluid capacity of the fuel mixing chamber and to correspondingly regulate the amount of air which is drawn into the chamber on every non-working stroke of the piston-hammer.

A further object of my invention is to provide a construction wherein the section of the cylinder forming the explosion chamber and the cylinder head therefor may be readily removed and replaced upon the other parts of the mechanism when assembled to expose the piston-head as, for example, for the replacement of piston rings, without disturbing in the least the assembly or adjustment of the other parts of the device except possibly the upper ends of the guard rods or frame by which the device may be carried from place to place and steadied during -the operation of the device.

A. further object of my invention is to provide the cylinder of an impact tool of the type above described, with three chambers in each of which is a piston-head of the piston-hammer. the three chambers forming respectively the explosion chamber, the air compression chamber and the fuel mixing and transfer chamber, without necessitating the use of a stationary cylinder head between the piston-head and the. hammer head.

A further object of my invention is to so position the carburetor with respect to the cylinder and the guard frame that it is shielded or protected from accidental knocks and the injury likely to result therefrom, the carburetor being positioned below the overhanging oil pan and between the rods or bars which support the knee-plate, and behind the knee-plate. V a v A further object of my invention is to provide the housing for the flywheel or rotor element with a receptacle within which is fitted and retained an ignition unit comprising the induction coils and condenser. whereby said unit may be located close to the spark plug and electrically connected therewith by a short insulated wire which is not in the way of the operator and which is not subjected to the rubbing, bending or flexing that a long connection for the purpose would be subjected.

A further object of my invention is to dispose substantially all the bolts or fastening means by which the parts are connected together with their longitudinal axes substantially parallel to the axis of the cylinder, so that the severe shocks and blows to which the parts are subiected and which are in the main in a direction parallel to the axis of the cylinder, may e taken up by the bolts longitudinally, thereby avoiding the tendency of the fastening means to shear when subjected to such stresses.

The severe vibration to which the crosshead and the piston-hammer are subjected makes it difficult to mount the cross-head in the piston-hammer in such a way that it does not creep slightly longitudinally and loosen as a result of such stresses. It is the object of my invention to prevent such motion or loosening of the cross-head by tightly fitting it into a cylindrical passage through the pie ton-hammer with a spline to prevent the rota- I tion of the cross-head about its axis and to hold it in position by a slowly tapering pin tightly fitting a corresponding tapered hole passing transversely through the piston-hammer and forming a tangential groove in the surface of the cross-head. When said pin has been tightly driven into said tapering line supply tank, carburetor, supporting rods or frame by which t e tool may be handled or manipulated and operated, and the knee-plate shown in elevation.

Fig. 2 is a side elevational view of the rear side of the tool shown in Fig. 1 with the knee-plate removed. v

Fig. 3 is a top plane view of the top plate or cover and the supporting handles or bars attached thereto;

Fig. 4 is a Vertical sectionalview through the timing mechanism and a diagram of the electric ignition circuit connected thereto.

- Fig. 5 is a vertical section through the car buretor.

Fig. 6 is a side elevational view but with a vertical section taken throu h the gasoline needle valve portion thereof said section being on the line6-6 of Fig. 5.

Fig. 7 is a horizontal sectional view through the cylinder and through the air pressure controlling valve for the air compression chamber, said section being substantially on the line 7-7 of Fig. 2. I i

Fig. 8 is a vertical sectional view on the line 8-8 of Fig. 7.

Fig. 9*is an end view of the pressure controlling valve, the lower part being broken away or sectioned to show the dirt and dust deflector over the air inlet port or opening.

Fig. 10 is a vertical elevational view of the cam mechanism and cross-head of the motor.

Fig. 11 is a vertical sectional view of the upper part of the hub of the rotor.

Fig. 1 2 is a similar vertical sectional View of the lower part of the hub of the rotor.

Fig. 13 is a detail, partly in section, of the closure for the fuel tank.

Fig. 14 is a detail view of the adjustment for the needle valve of the carburetor.

Fig. 15 is a plan view of the top of the main sleeve of the tool holding chuck.

Fig. 16 is atop plan view of the upper ring or washer of the tool holding chuck.

Fig. 17 is a top plan view, partly in section,

of the lower ring or washer of the said chuck with that part of the chuck which passes through said ring shown in transverse crosssection.

Fig. 18 is a side elevational view, partly in section, of the lower ring or washer shown in Fig. 17

F ig. 19 is a detail, mostly in section, showing the cross-head pin passing through the cross-head supporting section, the rollers, the manner of securing the cross-head pin rigidly in the cross-head supporting section of the piston-hammer and the rollers mounted and retained on the cross-head.

Fig. 20 is a fragmentary view of the crosshead supporting section with the cross-head in cross-section, the section being taken at right angles to that shown in Fig. 19.

Fig. 21 is a transverse sectional view of the piston rod with the split sleeve clamped thereto fondetermining the capacity of the air compression chamber. 1

Fig. 22 is atop plan view and Fig. 23 a side elevational view of one of the springs of the chuck.

Fig. 24 is a horizontal cross-sectional view of a part of the explosion section of the cylinder, showing the exhaust ports and the deflectors secured on opposite sides thereof; and r Fig. 25 is a longitudinal sectional view, similar to Fig. 1, of a modified construction.

Referring first to the construction illustrated in Fig. 1, the main cylinder 1 is preferably composed of three generally cylindrically-shaped alined portions, namely, the combustion or explosion end or section 2, the cross-head guide and rotor supporting section 3, which. is an intermediate section, and the fuel intake and compression section which is the lower section 4.

In the form of myinvention illustrated in Fig. 1, the fuel intake and compression end or section may substantially comprise two parts, namely,-(1) the fuel mixing and transferring'chambcr 5 and (2) the air compression chamber 6.

The piston-hammer 7 is a unitary piece of steel, comprising substantially an explosion pisto1i8-fitting the combustion explosion end chamber 5. The piston 12 similarly fits'amt reciprocates in the air compression chamber (l of the fuel intake and compression end 3 or section 4. The piston rod 13 connects the cross-head supporting section with the pisten 11 and the cross-head section 9 with the explosion piston 8. in the upper or combustion end 2 of the cylinder 1. The combustion or explosion end or section 2 of the cylinder is provided with a circumferential flange 14 adjacent but spaced upwardly from its lower end, and below said flange, the portion 15 is cylindrical and is made to carefully fit into the cylindrical upper end of the intermediate or rotor supporting section 3 with the bore' in the upper section 2 in strict alinement with the axial passage through the intermediate section 3.

The upper end of the explosion section 2 is closed by a cylinder head 16, which is tightly retained in place by studs 17 passing through the flange 14 and threaded into the peripheral flange 18 at the upper end of the intermediate section These bolts or studs 17 are preferably provided with intermediate heads 19 which draw and hold the flange 14 tightly against the flange 18 and the studs 17 are preferably prevented from becoming loose by suitable lock washers 20. Above the inter- -mediate heads 19, the studs 17 pass upwardly through openings through a circular series of thin fins or flanges 21 arranged circumferentially around the upper end of the explosion section 2. These fins 21 provide an extensive surface from which the heat transmitted thereto is dissipated into the surrounding atmosphere. The cylinder head 16 is also preferably provided with a series of similar thin fins 22 disposed radially from the center thereof, for dissipating into the air the heat communicated to the cylinder head from the combustion of the fuel.

Between the fins 22 and in alinement with the studs 17, the cylinder head 16 is provided with sleeve-like spots or lugs 23 formed integrally with the has 22 and cylinder head and provided with holes through which the upper ends of the studs 17 pass. The upper ends of the said studs 17 are preferably screwthreaded and provided with nuts 24. The center underside of the head 16 is provided with a cylindrical projection 25 fitting tightly into theupper end of the bore in the explosion section 2 and a suitable gasket 26 tightly closes the upper end of the cylinder. The cylinder head 16is also provided with another spot or boss 27 integral with and connecting two or more of the fins 22 and pro- \'ided with an opening 28 therethrough into which is fitted a spark plug 29.

Between the studs 17, the flanges 14 and 18 may be clamped together with shorter studs 30, screwthreaded at their upper ends and provided with nuts 31.

Through the cylinder. wall of the top sec- (ion 2 is a fuel inlet port 32 and substantially alined therewith on the opposite side of the said cylinder wall is an outlet or exhaust port or ports 33 disposed as is usual in a two-cycle internal combustion motor. Around the ports 32 and 33, the adjacent fins or flanges 22 are cut away or dispensed with to provide flat seats against which, on the gas inlet side, 15 fitted a nipple member 34 with a passage therethrough in registration with said inlet ports 32 and screwthreaded to rece1ve the upper end of the fuel transfer pipe 35. The nipple member 34 is held against the flat surface surrounding the inlet ports 32 by a pair of bolts 37. the heads 37 of which lie fiat against a flat surface provided around the outlet ports 33, and having nuts 38 on the mlet side for drawing the nipple member 34 tightly against its seat. On the exhaust or outlet side are provided a pair of sheet metal deflectors 36, (see Fig. 24) havin a trough or channel 39 on the front thereot adjacent the flatsurface around the outlet ports for reception of the heads 37 on the bolts 37. The walls of this channel fit against the sides and top of the head 37 and the said deflectors are held firmly against said flat surface by a screwthreaded extension 37" onsaid bolts passing through an opening in the bottom of said channel, and a nut 37 firmly drawn against the outside of the projection formed by the channel 39 pressed into the members. From a point adjacent the heads 37 of the bolts 37 the deflectors 36 are provided with substantially flat wings converging toward each other to direct the spent or exhaust gases outwardly between the wings and the fins above and blow them away from the hands of the operator, and to keep dust from collecting around and entering the parts 33. Between the nipple member 34 and the seat therefor may be interposed a suitable gasket 40 for securing a tight joint in the gaseous fuelconduit at that point. Lock washers 41 are preferably clamped between the nuts 38 and the nipple 34 to prevent any loosening of the nuts and the parts held together thereby, by reason of the intense vibration to which the tool is subjected while inoperation.

The fins 21, 22 are thin and provide a large heat radiating surface and are integral with the metal forming the cylinder walls and the cylinder head. These fins are in continuous metallic engagement with the cylinder and substantially with the piston. Heat is also conveyed or conducted from the cylinder and piston. through the flange 14 directly to the cover 42, lying on and secured to and held in direct metallic engagement with the periphery of the said flange by the bolts or screws 43. Some of the heat of combustion \Vlll be also conveyed directly from the lower end of the cylinder 2 into the intermediate section 3 which is also in direct metallic contact therewith. 'lhe explosion piston 8 is preferably provided with a plurality of relatively wide piston rings 44 maintained in direct metallic contact with the cylinder walls and the piston so that the heat of the piston maybe conduct- 9 ed directly therefrom to the cyllnder walls 2 and thence to the parts which are in direct metallic contact therewith. But even with these provisions and expedients, the temperamake the combustion or explosion end or section 2 of the cylinder 1 of steel heat-treated in such a way as to make it very strong, tough and hard at thehigh temperatures to which it is subjected in operating the drill. As a mat ter of fact, in making the three main members or sections 2, 3, and 4, I preferably used diflerent kinds or grades of chrome nickel steel all differently heat-treated to make each part or section best suited for the conditions of heat and vibration to whichit is subjected during the operation of the drill. Thus, the to or explosion section 2 is a drop-forging of arpenter steel #5-317, chrome nickel steel, heattreated before machining by heating the foliaging to a temperature of 1450 F. to 1475 quenching it in oil and then drawing it back to a temperature of from 900 F. to 1000 F. This heat treatment is effected before the piece is machined.

The intermediate or metal rotor supporting section 3 is a drop-forging of Carpenter #3 317 chrome nickel steel, heat-treated after rough machining and after finishing the surfaces of the guide slots 47 for the crossheads. The faces ofthese slots are first all carburized or case hardened in a carburizing box at temperatures between 1600 F. and 16509 F. while the rest of the forging is protected by handing or clay packing. The forging is allowed to cool in the carburizing box after. which it is heated to a temperature of from 1550 F. to 157 5 F., quenched in oil, reheated to a temperature of from 1350 F. to 13? 5 F., quenched in oil and drawn at 900 F. The fuel andintake end or section 4 of the cylinder is also a steel drop forging, preferably of Carpenter chrome steel #5-317, but in this case the heat-treatment follows the rough machining of the part and is for toughening the steel, particularly on account of the shocks or vibrations which it is required .to absorb. This forging is preferably heated to a. temperature of from 1500 F. to 1525 F.. quenched in oil and drawn to 1000 F. In

this Way the steel-of each of the three main sections of the cylinder 1 are different in the completed cylinder. Each section is made so as to withstand the peculiar continuous severe vibration to which the drill, as a. whole, is

- subjected, even under the relative higher temperatures to which the explosion end of the cylinder is subjected, the heat of said explosion end being conducted through the metal throughout the whole cylinder but to varying degrees. When the arts are made in the manner above descri ed, I have found the drill to operate in a highly satisfactory man- In the foregoingthe steels which are pref-' erably used in the construction of the three parts of the cylinder have been referred to by the terms used in the trade. Carpenter steel of the No. 317 type is a chromium nickel steel containing chromium 1.00% and nickel 1.75%

and thus corres onds in alloy content to the S. A. E. Series 0. 3200 (Society Automotive Engineers Series). In the Carpenter series the numeral before the hyphen indicates the gpproximate carbon content, just as in the A. E. series the last two numerals indicate the same carbon content. Carpenter steel N 0. 5-317, chrome nickel steel contains sub stantially chromium 1.00%, nickel 1.75%, carhon 50% and corresponds substantially to S. A. E. steel No. 3250. Similarly, Carpenter steel N 0. 3-317, chrome nickel steel contains chromium 1.00%, nickel 1.7 5%,carbon .30% and corresponds to S. A. E. standard No. 3230 chrome nickel steel. It is to be understood, however, that I do not wish to be limited strictly to the exact steelsabove mentioned nor to the exact treatment, the above being given by way of example of one manner in which the invention herein described may be put into practice.

Near thelower end of the upper section 2 and surrounding said section and seated on the underside of the flange 14 and between said flange 14 andthe u per ball race 45, is a laminated shim or was er 46 of the proper thickness to insure the fit of the parts.

The intermediateor rotor supporting section 3 is in the main circular in cross-section, but it is provided with a pair of parallel slots or guideways 47-47 diametrically opposite each other and extending parallel to the axis of the cylinder. I preferably provide inwardly directed parallel flanges 48 extending inwardly from the vertical side edges of the slots 47. The lower end 3' of the section 3 is preferably a little larger in diameter both outside and inside than that of the portion containing the slots 4747, thereby providing two stepped peripheral flanges, 49, 50, respectively, namely, the'flange 49, spaced from the lower end, and the flange 50 at the lower end of the section 3. Seated on the upper stepped flange 4.9 is a ball-race 51; seated on the upper side of the stepped flange 50 and surrounding the section 3' is the oil pan 52;

and bolted against the lower face of the 54, clamp together the said ring or washer 54, the bottom edge of the pan 52, the flange and the'flange 53, and serve to rigidly connect the lower section 4 with the lower end of the intermediate section 3. Preferably, lock nut washers are inserted or interposed between the nuts 56 and the flange 53 to prevent the loosening of the bolts by the vibration of the machine when operated. The upper flange 49 near the lower end of the intermediate section 3, makes the diameter of the opening at the extreme lower end of the said section, larger than it isabove said flange. For the purpose of securing exact alinenient of the lower section 4 with the intermediate section 3, the upper cylindrical end 57 of the lower section 4 extends into and tightly fits within the axial bore of the intermediate portion 3 above the flange 49, and an annular flange 58 on the upper side of the flange 53 fits within the larger part of the said bore below the flange 49. Thus the fuel intake and compression section 4 is also provided with a cylinder 60, preferably of smaller bore and which, with the hammer-head 10 and the closure 61 for the lower end of the said cylinder, forms the air compression chamber 6. The closure for the lower end of the cylinder 60 is the anvil 61 in which is slidingly mounted the strike-pin 62 provided with a small axialbore 63 therethrough and at its lower end with a head 64 squarely fitting against a shoulder 65 formed by the counter-bore 66' at the lower end of the bore 63. The head 59 of the anvil 61 rests squarely against the lower end of the cylinder 60. The cylindri cal surface of the anvil 61 is provided with a plurality of circumferential channels 67 which, during the operation of the machine are maintained filled with oil, thereby making an airtight seal between the interior of the chamber 6 and the exterior of the anvil 61. The chuck 68 is provided with aplurality of coiled springs 69 (one only is shown) bearing against the upper surface of the flange 7 O at the lower end of the cylinder 60 and compressed between said flange and a nut 71 on the upper end of a bolt 72 passing through said flange and through arms 73 extending radially from the top edge of the chuck 68.

The cross-head supporting section 9 of the piston-hammer 7 is substantially rectangular in transverse cross-section with the corners 74 between the straight sides rounded or arcuate. It is provided with a cylindrical bore 75 extending straight through it at right angles to the axis and piston with a keyway 76;

and with a transverse tapering hole 77, circular in cross-section, the axis of which is preferably tangential to the bore 75 and this hole 77 is preferably disposed in a plane at right angles to the axis of the hole 75 and passes through the axis of the piston-hammer 7.

This tapering hole 77 (see Fig. 20) is prefder 1.

erably drilled or formed after the cross-head pin or stud 78 has been positioned in the cross-head supporting section 9 and will be referred to again below. The cross-head pin or stud 78 comprises a middle or central portion 79 of uniform diameter and of a length equal to the length of the bore 75 through the cross-head supporting section 9. On each side of this middle portion 79, the cross-head pin is provided with a cylindrical section 80-8O of slightly reduced diameter forming journals upon which are mounted to rotate steel rollers 8l--Sl respectively of preferably a diameter equal to the width of the flanges 48 along the opposite vertical edges of the slots or guideways 47-47 through the walls of the rotor supporting section 3 of the cylin- At the outer ends of these journals 80--80, the cross-head pin or stud 78 is again slightly reduced in diameter to form journals 82-82 for steel rollers 8383 respectively and outside of these rollers are cylindrical rings 8585 rigidly secured to the ends of the cross-head )in 78 by tapered pins 86-86 tightly drawn 1nto correspondingly tapered holes through said rings 85-455 and through the ends 82-82 of the cross-head pin or stud 78. The middle or central portion 79 of the cross-head pin 78 is provided with a key 87 which fits into the keyway 76. The fit of the intermediate portion 7 9 of the pin within the bore or hole 75 is a tight driving fit, the key 87 fitted into the keyway 76 being operative to prevent the pin 78 from turning on its axis while it' is being drawn into the hole 75 or after it is in position therein. When properly positioned in the cross-head supporting section 9 with the ends of the intermediate portion 79 flush with the outer surfaces of said portion, the tapered hole 7 7 is drilled or formed through the cross-head supporting section 9 and through the outer surface of the cross-head pin or stud 78 and after the tapered 'hole is so formed, a tapering pin 88 is driven tight into said hole. Thus, the key 87 and keyway 76, together with the frictional engagement between the cross-head pin and the cross-head supporting section 9 prevent any rotational movement of the pin within the cross-head section 9, and the tapering pin 88 cutting through the surface of the cross-head pin 78 prevents any longitudinal movement of the cross-head pin and the parts are rigid- .l v secured together in such a way that they will not work loose notwithstanding the severe vibration to which the drill is subjected during the operation thereof. The rollers 8l81 are substantially anti-friction rollers and serve to reduce the wear between the cross-head pin and the guide slots 47-47. the walls of which are case hardened. The rollers 83-83 cooperate with a cam path 85) formed between the upper part 90 and the lower part 91 of the cam cylinder 92.

The hub or rotating member 93 upon which the cam cylinder, is mounted, is also made preferably of two arts, the'upper part 94 being secured to t a lower part 95 by a series of studs 96 rigidly secured to a flan 98 on the lower part 95 and passingjthroug a cooperating flan e 97 on the upper part 94 and held thereto y nuts 99 provided with lock nut washers 100. To the innercylindrical surface of the lower part 95 of thehub member93, the lower part 91 of the cam 92 is fitted and secured rigidly in place by rivets".

' 101--101. The lower edge of the. lower part 91 of the cam 92 is seated a inst a square shoulder 102 in the lmbPOItl-D1195p In the same way the 11 per portion-90 0117116 cam cylinder 92 is tted within andg is; ,rigidly secured to the inside of the-upperpart'flliof the hub or rotating member 93 beingl'provided with a shoulder 103 bearing 'a ai-nst the inner edge 1 of the opening'throu I v extending flange 104 near eupperjend oi otetin'g more-orless independent cam surfaces 105- 109-j respectivelyn The cam sent nce on the lower part 91 is preferably :the'fonly sure face which is in substantial engagement with thecam rollers 83 when the device is operating b thefe'xplosive action or a gaseous mixture, in theexplosion end or section 2 of the cylinder 1. The cam surface 105 of the upper portion 90' of the cam cylinder is in the main for the purpose of cooperating with the said rollers 83 in starting the motor by manually rotating the flywheel and so forcing the piston-hammer 7 downwardly to efiect an intake of gaseous mixture in the explosion end of the cylinder. Both cam surfaces 105 and 106 are respectively duplex in character, that is to sayeach camsurface is repeated on diametrical y opposite points of the axis of the cams and. ven exactly the same contour or outline so that during a complete rotation of the cam, the cam follower rollers 83--.83 and consequently the piston-hammer cooperating therewith will make two complete reciprocations for every revolution of the cam.

.The inner surface of the lower part 95 of the hub 93 is provided with a thickened portion 95', (see Fig. 12)., the upper ed of which parallels generally but is'space a little below the cam surface 106 of the cam 91. To

this thickened portion 95" the lower part 91 thickened portion 94' and the lower edge thereof-generally parallels but is spaced slightly above the cam surface 105 of the cam.

and tothis thickened portion, the part 90 of the 'cam' cylinder is'similarly secured by rivets or screws 107 in holes 107', as indicated in Figs. 10 and 11. The characteristic features of the cam surfaces 105 and 106 will be referred to again below. v

Above the flange 104 in the up of the hub 93 is a square seat or s oulder 108' (see Fi 11) in which is seateda ballv race 109, an a-series ofanti-frict'ion balls 110 are suitably interposed between the ball races 45 and 109 respectively. It is referably u on this upper part or half 94 o the hub 93 t at the balance or momentum wheel 111 islcarried, preferably integrally with the hub portion 94. The lower end of the lower art of the hub is preferably recessed annu arly to provide a square shoulder or seat 112 for a ballrace 113 forming a part of an anti-friction hearing which also includes the anti friction balls 114 and the ball race 51-seated on the upper stepped flange 49 at the lower end of the intermediate rotor supporting section 3. Thus it is that the cam cylinder 92 as a whole, the hub 93 as -'a "whole and the balance or momentum wheel 111' and the parts carried thereby constitute the rotor 116 of the mechanism by which the rectilinear reciprocatory motion of the piston-hammer 7 produces a rotary movement of the rotor 116. The energy thus stored in the rotor is used to effect the return or compression stroke of the piston-hammer, as well as to control and o crate the timing mechanism 117 of the ignltion system of the motor.

.Above the rotor 116 and rigidly secured to the upper side of the flange 14 of the combustion section 2 is an annular cover 42, the

lower edge of which generally extends downwardly and lies close to the upper surface of the rim oi: the balance or momentum wheel 111 but. said cover 42 is provided with a pair of diametrically oppositely disposed recesses 120-120 provided with strengthening lugs 121 in the inner walls thereof, providin vertical flat faces 121 '121 upon whic are secured the inner ends 122' of handles 122-122 by suitable bolts 123, 123.

The cover42 is also preferably provided with'a seat or pocket 124 cast integrally therein of a size and shape to seat and hold an ignition unit 125 comprising a suitable inductlon coil 322326 and condenser 328 for the ignition system of the mechanism and referred to again below. This ignition unit 125 when placed in the seat or pocket 124 in the cover 42 is not far from the outer end of the spark plug 29 so that a single short insulated electric conductor 126 may be employed to connect the coil with the spark plug. When so disposed, the conductor 123 maybe rigidly secured to the binding posts 127 and 128 of the spark lug and electric unit respectively and that s ort connection will not be subject to twists or excessive vibration and consequent frequent rupture while the drill is in operation. The conductor 126 is out of the way. I tis not liable to be caught on objects close to which the drill may be brought, or with the hands, or arms of the operator, for it is out of the way, fairly well protected by the framework by which the drill is guided, held and carried from place to place as will be referred to again below; The likelihood of breaking the electric circuit by breaking the conductor 126 or detaching it from the binding posts 127 and 128 is greatly minimized.

tion as to pass directly under the contact device 117, are two relatively small steel plates 132, diametrically disposed with respect to the axis of the balance wheel (only one is shown in Fig. 1) and rigidly secured thereto by a bolt 119 and a steady pin 130.

Each plate 132 is provided with a narrow substantially radially extending tapering projection 133 so that as the plates successively pass under the contact maker 1.17 the projections 133 will engage a vertically slidahle rod or plunger 134 in the contact maker 117 and lift the same to bring a movable contact point of the lower portion 185 of the contact maker 117 into engagement with a stationary contact point of the upper portion 136 of the contact maker 117 which is in electrical communication with a binding post 137 but which is insulated from'the cover 42.

. Because the binding post 137 is in the primary circuit of the ignition system of the tool, the primary circuit will thus be intermittently closed by the contact maker 117. Preferably this contact makerll'r' is enclosed by a small metallic cover 138 which fits over and closes the recess or space 129 in the annular cover 42.

The oil pan or casing 52 is preferably substantially circular in horizontal cross-section. Tn vertical cross-section it slowlycurves from the edge of the circular opening through the bottom thereof upwardly and outwardly to a point near the top thereof and its upper edge 139 is then curved inwardly and downwardly close to the outer circumferential surface of the hub 93. The flange 98 at the top of the lower portion 95 of the hub 93 is preferably provided with an annular recess 140 of the pan 52. \Vithin the pan 52 and near the bottom thereof is an inwardly extending continuous annular flange or ridge 142 form ing a shallow oil retaining chamber 143 into which project the lower ends of preferably two inclined oil conducting tubes 144. preferably diametrically oppositely disposed with respect to the axis of the rotor and passing upwardly through the thickened portions 95', 95 of the lower part 95 of the hub 93. The lower ends of the tubes 144 are in advance of the upper ends and when the rotor is rotating rapidly and the lower ends of the tubes 144 dip into the oil, the inertia of the oil will cause the tubes to scoop up the oil and the oil will substantially flow upwardly through the tubes and be discharged as a stream against the rollers 83 on the cross-head pin 78 and the cam edges 105 and 106, thus insuring a thorough lubrication of the cam surfaces 105 and 106, the rollers 83, 83 coacting therewith, the guideways or slots 47 and the rollers 81, 81 cooperating therewith. If for any reason the supply of oil in the pan 52 be allowed to be depleted and the drill is being used in a tilted position, that is, at an angle to a verti-' cal or perpendicular position, then the inwardly ehtcnding low annular ridge or rib 142 will retain a substantial quantity of oil in the pan in a position where the ends of the tubes 144 will stilldip into it on every revolu tion of the rotor and the likelihood of affording insufficient lubrication for the cams, cross-head and guideways is greatly reduced.

The upper inturned edge 139 of the pan is for the purposes of preventing oil from being spilled out of the pan when the drill is held or supported at a decided angle to the perpendicular and the similar inturned ridge or rib 142 insures the retentionofsutficient oil at the bottom of the pan whence it may be lifted by the rapidly revolving inclined tubes 144 when the tool is being used in such a position that were it not for the ridge or 'rib 142, all of the oil would flow to a place where the lower edges of the tubes 144 would not dip into it and lift it.

Extending outwardly from the side. of the pan is a snout or tubular inlet 145, preferably normally closed by a cap 146 and gasket 147, the cap being retained in place by a resilient bail 148, the ends of which are pivotally connected to the sides of the snout and the loop of which fits and looks or snaps into a recess or groove 149 in the top of the cap, when the cap is in closed position. It is through this snout or inlet 145 that oil may be introduced for the lubrication of the operative parts of the drill.

The chuck 68 is preferably in the form of a sleeve 150 having an axial hole 151 therethrough of any suitable shape in transverse cross-section, such as a square hole or a hexagonal hole to fit on, over and around the end of a tool insertible therein and correspondthe sleeve 150 and bearing against the shoulder 152 on the sleeve 15 0'adjacent the flange 73 is a ringor washer 153, preferably .provided with a downturned circular flange 154.

The hole 153' (see Fig. 16) through this washer is substantially of the size and shape of the exterior of the sleeve 150. Within the flange 154 of this washer 153 is fitted the upper end of a coiled spring 155 surrounding the sleeve'150 and having its opposite end normally pressing against a collar or retainer having a circular recess 159 in its lower face and fitting over and around a split ring 157. The passage 156 through the collar 156 is of the same sizeand shape as that of the outside of the sleeve 150. This split washer 157 is circular and preferably L-shaped in crosssection and its outer diameter fits into the cylindrical recess 159 in the lower side of the.

collar orretainer 156 and its innerdiameter fits a circular channel 158of,thesleeve 150 near the lower end of the *sleeve 150 and of a diameter slightly less than the distance between the parallel faces 150 -150. The L- shaped split ring 157 is seated in the groove 158 and is held there by the walls of the recess 159, in the lower r1ng,washer, collar or retainer 156. In this manner the partsof the chuck 68 are held together in their operative positions and relationship. On opposite sides of the ring or washer 153 pins or lugs 161 project in diametrically opposite directions and they are encircled by eyes 162 von the end of a drill or tool retainer 163 which is thus pivotally mounted on said pins or lugs 161. The collar or retaining member 156 is widened on its rear sideadjacent the operator and is provided with a air of substantially semicircular recesses 160 into which the parallel lengths of the tool retainer 163 snap and by which they are retained in .place to hold the drill in the chuck 68, as is clearly indicated in Fig. 17.

For holding and steadymg the machine in operation, I have provided a framework made oftwo tubular rods 164 connected together and bent into convenient form and shape. These two somewhat complementally arranged rods 164, preferably consist of vertically-extending tubular portions 165, at the upper ends of which are. substantially horizontally extending portions 166 terminating directed lugs 168, 168 and are connected together by a hollow cross-bar 169, the ends of which are welded to the vertical portion 165.

' Below the vertical portions 165 the said bars verging1 portions 170 terminatin in eyes 171 adapte to fit against the opposite sides of a lug 118 extending rearwardly from the lower end of'the fuel and intake section 4 andare securely held in place by a bolt and nut 172 extending through the said lug 118 and v through the eyes 171.

Between the two main vertical portions 165 I and'pivotally mounted upon the cross-bar 169 is a knee-plate 173 which is preferably made of sheet metal and the lower portion 173' thereof is preferabl vertically concave, to substantially fit against the thigh or leg of the operator. This knee-plate 173 is pivotally mounted on the cross-bar 169 by straps or brackets 174 substantiallyencirclingthe crossbar 169 and secured to the knee-plate by bolts 175. The inwardly directed lugs or projections168 are engaged bgihe sides of a portion of the knee-plate 173 a vs the cross-bar 169, when it is in its substantially vertical posi tion and are operative to prevent further rotative movement of the knee-platein an anti clockwise direction. These lugs 168 serve as stops to prevent the movement of the u per part of the knee-plate inwardly towar the cylinder after it engages with the lugs'168. By means of the hand es 122 and the framework partlysupporting the tool on the thlgh by theknee-plate 163 an operator may with facility carry, hold, direct, steady and guide the tool in usin' the same. I 1

Secured to t e horizontal upper ortions 166 of the framework are a pair of rackets 176. These are preferably made rigid with the frameby spot welding and upon these brackets is mounted and supported a tank or fuel reservoir 177 of light steel sheet metal construction and provided with lugs 178- 178 which rest upon the brackets 176 and are secured'thereto by bolts 17 9'-17 9. The tank 177 is preferably provided with a snout or a filling tube 180, the upper end of which is arran ed to be closed by a suitable cap'181 and ,resi ient bail 182. Between the cap 181 and the end of the snout 180 is preferably interposed a gasket 183 (see Fi 13). .The cap, bail and gasket are prefera ly identical with those used to close the snout on the oil pan 52.

The bottom of the tank 177 is provided with a projection 177 to which is secured a a nipple 184 over which is threaded a cou-' pling 185 at the upper end of the gasoline feed pipe 186, the lower end of which is con nected by a coupling 187 to the upturned end of an elbow bracket or nipple 188.: This elbow bracket or nipple 188. is provided at its opposite end (see Fi 6) with a suitable flange 189 adapted to be tted tightly against a cooperating flange 190 on one end of the body 191 of the carburetor 192. The two flanges 189 and 190 are clamped together by bolts 193 with a gasket 194 clamped between said flanges. V

The carburetor 192 is composed in the main of two parts, namely, the carburetor body 191 and the carburetor cap 195. The carburetor body 191 is the part to which the gasoline supply pipe 186 is attached and it is provided with a longitudinally cylindrical hole 196 into which is threaded the needle valve stem 19?. The inner end of this hole 196 is provided with a shoulder 198 forming a seat for the pointed conical end 199 constituting the needle valve and beyond this shoulder 198 is a hole 200 of small diameter communicating at its other end with a counter-bore forming a chamber 201 which is in alincment with and communicates with the lower end of the elbow bracket 188 through the gasliet'194. At the right hand end of the carburetor body 191 there is formed a screwthreaded recess 202 into which is threaded the packing gland 203 serving to compress the packing 204 around and against the needle valve stem 19? to prevent leakage of gasoline around that end of the carburetor body. The outer end 205 of the needle valve stem is provided with an arm or lever 206 rign'dly secured thereto and serving as a handle by means of which the stem of the needle valve may be rotated to move the conical end 199 toward and away from its seat on the square shoulder 198. The end of the arm 206 is preferably provided with a plunger 20? which is preferably pressed by a spring 208 toward the carburetor and to hold the v -shaped or chiselshaped end 209 thereof into engagement with any one of a series of notches 210 arranged in an arcuate projection 210 on the right hand side of the carburetor cap 195 (see Figs. 6 and 14). As the arm 206 is manually swung to any desired position, the chisel shaped end 209 rides over the ridges formed by the notches or serrations 210 and when the valve 109 has been so properly adjusted the plunger member 209 is held in the coacting notch by the spring 208, thus holding the valve in its adjusted position whence it will not be moved by the vibration of the machine when operating. Communicating with the hole or chamber 196 and disposed at right angles thereto is a small duct or passage 211 which turns abruptly vertically and then extends laterally at an angle into and through the wall of the tapered valve seat 212 (see Fig. 6) on which is seated a valve 213 preferably provided with an axial cyllndrical stem 214 extending downwardly through a bearing 215 in which said stem 214 is longitudinally slidable. This bearing 215 is preferably formed in a bar or strut 216 which extends diametricallv across the opening 217 directly beneath the valve seat 212 and communicating with the atmosphere. Around this valve seat 212 and concentric therewith is a cylindrical wall or projection 218 over and around which is fitted the carburetor cap 195, the latter being secured to the body 193 by bolts 219 and nuts 219' as shown in Fig. 5. The carburetor body 191 is provided with a flat face 220 adapted to fit squarely against a flat face 221 of a projection 222 on the wall of the cylinder and through which is a passa e 223 communicatin with the fuel mixing and transfer chamber 5. There is preferabl a gasket 224 interposed between the two at faces 220 and 221. The bolts or studs 225 are provided with a shoulder or enlargement 226 drawn tight against the fiat face 221 by the screwthreads 225' on the end of the stud 225 and in the projection 222 on the cylinder wall. The holes 228 through the carburetor cap 195 are provided with a counterbore 227 at one end for the reception of the enlargements 226, and a counter-bore 229 at the other end for the reception of nuts 230,

by means of which the carburetor cap 195,

and the parts secured thereto are rigidly mounted on the cylinder with the gasket 224 compressed between them. The outer ends of the bolts or studs 225, pass through the flange 234 of the elbow 235 and are provided with screwthreads 231 over whichare treaded nuts 237 with lock washers 237' for holding the elbow 235 of the fuel transfer pipe 35 with its flat face 248 against the flat face 233 of the carburetor with the gasket 236 compressed between them. In this way the fuel transfer pipe 35 is put into direct communication with the passage or chamber 222 through the carburetor cap 195 over the valve 213. On the upper side of the valve 213 is preferably arranged an axial projection 238 around which is seated a coiled spring 239, the upper end of which also preferably surrounds a projection 240 formed on the upper wall of the chamber 232. The function'of the light spring 239 is to normallv hold the valve 213 on its tapered seat 212. Extending through the upper wall of the cap 195 and preferably in axial alinement with the valve 213 and its seat, is an adjusting screw 241, preferably provided with a lock nut 242. The lower end of this screw 241 is normally adjusted to a position slightly above the top of the projection 236 on the valve 213 and serves to limit the vertical movement of the valve when lifted off its seat.

The cubical capacity of fuel mixing and transfer chamber 5 is determined by the diameter of a split cylindrical sleeve .244 extending the full distance between the pistons 11 and 12 of the hammer-head clamped around the piston-rod section 13. The two halves of the split sleeve 244 are held to- 5 gether around the rod 13' by bolts 245 passing transversely therethrough (see Fig. 21). The space between the outer surface of the sleeve 244 and the inner walls of the fuel mixing or transfer chamber 5 at the end of the upward strokb of the piston-hammer constitutes the capacity of the chamber. If the capacity of the chamber be found to be insuflicient, a smaller sleeve 244 will be similarly clamped to the piston-rod section 13. If the amount of air taken in the said cham? her 5 be too great, then a larger sleeve will be similarly secured to the piston-rod 13. In this way the amount ofair taken into the chamber 5 may be determined and made to be exactly right and unvariable for the eX- plosive mixture. It is to be understood, of course, that the diameterof the chamber 5 is such that a sleeve 244. of greater diameter than the hammer-head 10 will never be.

needed.

In the form of my inventionillustrated in Fig. 1, the lower end of the hammer-head 10 is the piston 11 which fits into the chamber or cylinder 6 forming the air compression chamber. To admit air into this chamber, the wall thereof is pierced by a port 246 which passes through the wall of the cylinder and through a lug or projection 247 extending outwardly from the outer wall of the cylinder and provided with a square face 248 against which is adapted to be rigidly secured the flat face 249 of the pop-valve or pressure regulating valve 250 with a gasket 251 between them. In Figs. 7, 8 and 9, this pop-valve 250 is shown as secured tightly up against the fiat space 248 of the projection 247 by screws or studs 252 rigidly screwed into the projection 247 and passing through holes 253 through the casting. of the popvalve 250, (see Fig. 7 and as provided at their free ends with lock nuts 254, and with lock washers 254 preferably interposed between the nuts 254 and the valve body. This pop-valve 250 comprises a casting provided with a relatively large cylindrical chamber 255, the upper part of which communicates directly with the airport 246' by apassage 256. Within this cylindrical chamber 255 is fitted a cylindrical sleeve 257 having in its upper or inner end a tapered valve sfieat 258 and having at its lower end a flange 259 secured to and held against the flange 260 at the lower end of the casting by one or more bolts 261 with nuts 261'. Seated on this valve seat 258 is a valve 262 from the lower side of which preferably extend a circular series of fins or guides 263 slidingly fitting against the cylindrical passage 264 through the sleeve 257. A cylindrical projection 265 is preferably provided on the upper side of the valve 262 around which is fitted the lower end of a coiled spring 266, the upper end of which presses against the upper wall of the chamber 255 above the valve. I preferably also secure to the bottom of the cylindrical sleeve 259, a deflector 267 of preferably sheet material, preferably inclined downwardly and inwardly toward the axis of the cylinder and terminating in a'horizontally disposed upwardly inclined hell or mouth 268 so that the dust blown upwardly from the hole being drilled will not be drawn directly into the pop-valve 011 every upward reciprocation of the piston 11;" and so that the heavier particles of dust'will be prevented from entering her 270 and the outer end of this rod 272 is I provided with a winged member 274 somewhat resembling a winged nut but rigidly secured to the outer end of the piston-rod 269, the chamber 255 272 as by a pin 275. The head or cap 273 is secured to the casting (to close the cylindrical chamber 27 0) by screws 276. Between the piston 271 and the head 273 and surrounding the rod 27 2, is a coiled spring 27 7, under compression, tending to force it toward the opening or passage 278 and to hold a valve 279 on the end of the piston-rod 272 against its seat 280. This valve 279 when on its seat 280 closes the passage 278 leading from the cylindrical chamber 262. The outer surface of the head 273 is provided with a circular annular projection 281 preferably concentric with the axis of the piston-rod 27 2 but the outer end of which is provided with complementally diametrically disposed inclined edges 282, the inclination, however, being comparatively slight. These inclined edges 282 substantially form slowly rising cam surfaces and they are preferably provided with diametrically disposed grooves or notches 283 into which fit the adjacent edges 284 of the wings'285 of the Winged member 274. Wb en the winged member 274'is rotated slowly over the inclined edges or cams, the inner edges 284 of the wings will be forced out of one pair of diametrically oppositely arranged grooves 283 into the next pair of grooves and when the said member is rotated in a clockwise direction, reference being bad to Fig. 6, then the succeeding grooves will be more and more remote from the flange of the cylinder head or cap 273 and this upward movement will slightly lift the valve 279 from its seat 280.

In this way, the position of the valve 279 with threaded hole 287 therethrough into which is fitted the stationary contact screw 28 8 provide at its lower end with a tungsten tip 289.

The holder 286 is provided with a flange or bracket portion 290 adapted to be seated and held upon the vertical wall 131 by. the bolt and binding post 137. The bracket or flange 290 is, however, insulated from the cover 42 by a sheet or plate of insulating material 291 between the holder 286 and the wall 131, and the bolt 137 which passes through the wall 131 of the cover is also insulated therefrom by suitable insulating bushings 292 between them and the cover 42. The nut 137 secures the bracket 286 stationary with respect to the cover 42 and the inner end of the bolt 137 is provided with a nut 293, thus making of the bolt a binding post for the connection thereof with the electrical system of the device. Below this stationary contact member 136 is the movable contact maker 135 which consists of a metallic housin 294 securely fastened to the lower part 0% the wall 131 by bolts 295 passing therethrough and threaded into the metal of the cover 42. Within this housing 294 is a timer plunger shell 296 also of metal and having a vertical passage therethrough providing a shoulder 297 near the lower end thereof. This shell 296 is also provided with an axial passage therethrough of two diameters, the lower portion of the said hole being of the smaller diameter to provide a shoulder 298 therein upon which is normally seated the annular flange 299 of the timer plunger 300. The upper end of the passage or bore through the timer plunger shell 296 is preferabl counter-bored somewhat to provide an annu ar shoulder 301 near the top end of the shell for the reception of a washer 302 and the disk-like flange 303 of the timer plunger bearing 304. The upper end 305 of the timer plunger shell 296 is prefv erably made thin so that after the parts are assembled in the shell the said upper edge 305 may be spun over inwardly against the upper surface of the flange 303 to retain the timer plunger bearing 304 fixedly inposition within the shell. Between the upper surface of the flange 299 of the timer plunger 300 and the washer 302 is a coiled compression'spring 306 tending to normally hold the flange 299 on its shoulder or seat 298 and the lower end of the plungeron or close to the plane surface of the plates or rings 132 and in the path of the projections or knife edges 133.

Just above the plane of the surface of the upper ends of the timer housin 294 and below the thin upper edges 305 of t e shell 296 is provided a shoulder 307 upon which is seated a plate or washer 308 through which the upper end of the shell 296 passes, said plate being secured to the upper surface of the housin 294 by suitable screws 309. The purpose 0 this plate and screws is, of course, to permanently hold the shell 296 within the housing 294. In Fig. 1 I have shown the timer or contact maker 117 and the ignition unit 125 as being diametrically oppositely disposed on the cover and in the plane passing through the axis of the cylinder and midway between the verrecesses to receive both the contact maker and the electrical unit on the rear sideof the machine adjacent the operator in the manner shown in Fig. 3 for in this way the timer and electrical unit are brought close to each other and to the spark plug 29, to provide short connections 126 and 324 between the electrical'unit and the binding posts 127 and 137 res ectively;

n Fig. 10 is shown the cam cylinder 92 comprising the upper portion and the lower portion 91. The lower portion 91 provided with a cam surface 106 is substantially the only cam surface which is operative during the normal operation of the drill after it has once been started. It will be plain that with such cams as have been above shown therein, there will necessarily be two complete reciprocations of the piston-hammer for every revolution of the rotor. From the high point 310 of the cam portion 91, the cam path 106 is provided with a steeply inclined portion 311 which extends for a little more than one-half the stroke of the piston-hammer and this inclined portion 311 terminates in an abrupt drop 312 during which the roller 83, cooperating therewith, is out of engagement with the cam 91 up to the end of the stroke. From the lower end of the abrupt drop portion 312, the portion 313 is a slowly rising surface up to the next high point 310 of the cam 91 and on the opposite side of the cam cylinder, after reaching which the cam surfaces 311, 312, 313 repeat back to high point 310 first above mentioned. During all this time, the upper portion 90 of the cam cylinder is preferably out of contact with the roller 83.

But the cam surface 105 of the portion 90 is preferably provided with a sharply descending portion 314 extending practically parallel to the steeply inclined portion 311 of the other cam 91 and down to a low point 315 which is so positioned that in starting the device the operator, by manually rotating the rotor 116 in the direction indicated by the arrow 316 will force the roller 83,- contacting therewith, downwardly and with it the crosshead 78 sufliciently to uncover the ports 32 to permit/the explosive charge to be supplied vided with holes 101' for the reception of the bolts or rivets 101 by means of which it is 

